1. Field of the Invention
The present invention relates to an inner bag for a transport tank and the loading method thereof.
2. Description of the Prior Arts
In cargo transportation by sea, railroad, road and so forth, a tank container is generally used for liquid materials (cargo). As the tank container, a 20 foot container (hereinafter referred to as a tank container) which conforms to the ISO Standards is ordinarily used, for example. The tank container has 20 foot length, 8 foot width, and 8 foot height, so that about 20 tons of liquid can be filled therein.
In the container transportation to use this kind of tank container, it is necessary to wash the inside of the tank after transportation, and in addition, to produce the tank by using a high quality stainless steel plate with chemical resistance. In order to solve the problems, Japanese Patent Laid-Open Publication No. S61-104983 discloses that an inner bag or liner bag made of soft synthetic resin to have the chemical resistance is loaded in the tank produced from the general steel plate. In addition, Japanese Patent Laid-Open Publication No. 2001-354292, Japanese Utility-Model Laid-Open Publication No. S61-48190, Japanese Patent Laid-Open Publication No. S50-4615, and Japanese Utility-Model Laid-Open Publication No. S57-46492 also disclose to load the inner bag in the tank in order to save the trouble for washing the inside of the tank.
However, with respect to the prior art inner bag to be used in the tanks and tank containers, it is so difficult to produce appropriate inner bags for large tanks including the 20 foot container that there has no practical application. Namely, it has been difficult to produce the inner bag fitting in the cylindrical 20 foot container easily and affordably. The ideal inner bag to fit within the tank container properly would be a cylindrical-shaped inner bag having approximately the same shape as the tank container. However, it is necessary to prepare circular lid films, and in addition, to weld the circular lid films on both ends of a tubular film. To make matters worse, since the circular lid film has to be welded not in a two-dimensional direction, but in a three-dimensional direction, the exclusive guide apparatus for welding the circular lid film is required.
In contrast, an envelope type inner bag is easily produced only by welding the both ends of the tubular film. This type of inner bag prevents the liquid from directly contacting with the inside of the tank by joining supply-discharge openings of the inner bag and the tank. Therefore, changing the inner bag makes it unnecessary to wash the inside of the tank. However, since the tank container is cylindrical, if the envelope type inner bag is loaded therein, the following problem occurs due to the difference in shape between them. If the envelope type inner bag has a capacity equivalent to or larger than that of the cylindrical tank container, the length should be made longer than the tank container. Accordingly, as shown in FIG. 14A for example, when an inner bag 2 is loaded in a tank body 3, an end portion 2a of the inner bag 2 incurves in the tank body 3. If liquid 6 is filled from a tank supply-discharge opening 5 in this state, since the tank supply-discharge opening 5 is formed in one end of a lower part of the tank 3, a bending line 2c of the end portion 2a is located adjacent to the tank supply-discharge opening 5. Thereby, as shown in FIG. 14B, the liquid 6 fills the end portion 2a preferentially, the tank supply-discharge opening 5 is plugged due to the weight of the liquid in the end portion 2a, so that the further filling of the liquid becomes impossible. Note that an element 7 is an inner bag suction preventing member. The inner bag suction preventing member 7 prevents the inner bag 2 from being sucked into the tank supply-discharge opening 5 in the final stage of discharging the liquid 6 to plug the tank supply-discharge opening 5.